What Are The Disadvantages Of Using JPEG Image For Texturing
It depends on what you want to achieve.
Basically, JPEGs are not all bad, especially for photographed image textures they work just fine.
Typical disadvantages of the JPEG format are:

Compression artifacts (should only be a problem if you have low quality or need very high detail)
No transparency channel (can be a problem if you want multiple overlaid textures or stencils)
Limited colordepth (for height- or bumpmaps or environment textures, the number of colors and/or brightness levels can be insufficient)

As advantages, I'd name the following:

It's usually the most readily available format for images (if you take or download a photo in JPEG format, you won't gain anything by converting it into another format)
For typical photographic images, it uses comparatively little space on your hard drive